Arteries and veins carry blood throughout your body, including your eyes. The eye’s retina has one main artery and one main vein. When the main retinal vein becomes blocked, it is called central retinal vein occlusion (CRVO).

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When the vein is blocked, blood and fluid spills out into the retina. The macula can swell from this fluid, affecting your central vision. Eventually, without blood circulation, nerve cells in the eye can die and you can lose more vision.